Calibration of a super-resolution display

ABSTRACT

A projector system includes an image generator and at least one projector for receiving an image from the image generator and projecting the image onto a screen to provide a final projected image. A computer generates correction data based on a calibration process that includes comparing an uncorrected image projected by the at least one projectors with a geometrically correct image. Wherein the at least one projector maps incoming pixel locations from the image generator to corrected pixel locations in the final projected image based on the correction data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/339,637, filed Jan. 26, 2006, the disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to calibration of a super-resolutiondisplay, in particular, a calibration method including geometrycorrection and color, intensity, brightness and uniformity matching.

BACKGROUND OF THE INVENTION

It is common in the projection industry to combine multiple overlappingdisplays from different projectors to produce arbitrarily large andirregularly shaped displays. Such displays are typically used inimmersive environments and large venues such as amphitheaters andshopping malls. The process of aligning and matching the projectors is adifficult and time-consuming task, which is typically performed by anexperienced installer. If the aligning and matching process is not doneproperly, an unsatisfactory image such as FIG. 1 a may be the result.Each projector image must align exactly to the pixel with its neighborsin order to produce an acceptable image such as FIG. 1 b. In theoverlapping region, where more than one projector is projecting, thebrightness levels of each projector must be controlled to achieve acontinuous image. Also, the colors of each projector should closelymatch in order to maintain the illusion of one continuous image.

U.S. Pat. No. 6,456,339 to Surati et al. and U.S. Pat. No. 6,222,593 toHigurashi et al. disclose the use of cameras and image processing tosimplify the aligning and matching process of the projectors. Ingeneral, these methods involve using information regarding the displayfrom a camera to program a “smart” image generator. The “smart” imagegenerator provides modified images with altered geometry, color andbrightness that are fed to a projector to produce a seamlessgeometrically correct image. The “smart” image generator, however, islimited to the capabilities of the calibration system rather than thecapabilities of the projector. By requiring all of the content to passthrough the “smart” image generator, latency may be introduced and theavailable content may be restricted. As such, a lower resolution displaymay result due to the maximum resolution of the calibration system beinglower than that of the original image.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a calibrationsystem for a single or multiple projector system. The calibration systemgenerates geometry calibration data that allows the projector system toreceive an image from an image generator and map incoming pixellocations to geometrically corrected outgoing pixel locations that areprojected onto a screen. The geometry calibration data is determinedthrough an iterative process in which a camera captures a screen imageof a matrix of projected reference markers. The locations of thereference markers in the screen image are compared with target referencemarker locations that are stored in a computer. New estimated locationsfor the projected reference markers are calculated and the process isrepeated until the reference markers captured by the camera are locatedwithin an acceptable distance of the target reference markers.

In another aspect of the present invention there is provided acalibration system for an image producing device. The calibration systemincludes a camera for capturing a screen image provided on a display,the screen image being provided by an image producing device receivingimage information from an image generator and a computer for performinga calibration process, the calibration process including comparing thecaptured image with a geometrically correct image and generatingcalibration data for mapping the image onto the geometrically correctimage. Wherein the calibration system is independent of the imageproducing device and the image generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the followingFigures in which like numerals denote like parts and in which:

FIG. 1 a is an image generated by an uncalibrated multiple projectorsystem;

FIG. 1 b is an image generated by a calibrated multiple projectorsystem;

FIG. 2 is a schematic diagram of a multiple projector system accordingto the present invention;

FIG. 3 is a flowchart showing an embodiment of a calibration process forthe multiple projector system of FIG. 2;

FIG. 4 is a front view of a display screen showing overlap betweenprojector images;

FIG. 5 is a view of a display screen from a non-centered eye point;

FIG. 6 is a flowchart showing the geometry correction process of FIG. 3;

FIG. 7 is a flowchart showing another embodiment of a calibrationprocess for the multiple projector system of FIG. 2;

FIG. 8 is a flowchart showing a brightness and intensity matchingprocess for the multiple projector system of FIG. 2;

FIG. 9 is a flowchart showing a uniformity matching process for themultiple projector system of FIG. 2;

FIG. 10 is a flowchart showing a color matching process for the multipleprojector system of FIG. 2;

FIG. 11 is a flowchart showing a blending process for the multipleprojector system of FIG. 2; and

FIG. 12 is a schematic diagram of another embodiment of a multipleprojector system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a is an example of an image generated by an uncalibrated multipleprojector system. The multiple projector system includes four projectorsthat project individual images. Because the multiple projector system isnot properly calibrated, the image in FIG. 1 a appears jumbled. FIG. 1 bshows the same image as FIG. 1 a, however, the image is projected from amultiple projector system that has been calibrated. As shown, the seamsbetween the individually projected images are undetectable.

Referring now to FIG. 2, a multiple projector system 10 and acalibration system 11 are generally shown. The system 10 includes fourprojectors 16 that receive image information from an image generator 12through respective video feed lines 14. Each projector 16 displays aportion of an image (not shown) on a display screen 18. The calibrationsystem 11 includes a camera 20, which is provided to capture an image ofthe display screen 18, and a calibration controller 22 that communicateswith both the camera 20 and the projectors 16. The calibrationcontroller 22 is generally a computer that generates calibration databased on a reference image, which is stored in memory, and digitalimages of the display screen 18 that are sent from the camera 20. Thecalibration controller 22 adjusts the individual image processingcharacteristics of each projector 16 in accordance with the calibrationdata in order to produce a geometrically correct image on the displayscreen 18.

Each projector 16 includes a warping system that is individually capableof color modification and geometry manipulation. The Matrix series ofprojectors from Christie Digital Systems may be used or any othersuitable warp-capable projector. The image generator 12 is an unalteredmulti-display image generator, such as SGI ONYX or Evans and SutherlandEPX System, for example.

Referring to FIG. 3, a flowchart of a geometric calibration process forthe multiple projector system 10 is shown. The embodiment shown in FIG.3 is for use with a generally planar display screen 18. At block 24, thelayout of the projection system 10 is sent from the image generator 12to the calibration controller 22, as discussed in detail below. Thelayout of the multiple projector system 10 includes the total imageresolution, which is measured in pixels, and the amount of overlap atthe intersection of every horizontally and vertically adjacent projector16. For example, an image produced by a six projector system is shown inFIG. 4. The image is made up of six single projector areas 36 thatoverlap one another at overlap areas 38. The image has a total imageresolution that is indicated by reference numeral 40.

The layout of the projection system 10 is obtained from the imagegenerator 12, which stores the information in order to properly dividethe image into multiple video feeds. The information is provideddirectly to the calibration controller 22 by the image generator 12through a cable (not shown) or through a wireless link. Alternatively,the layout of the projection system 10 may be entered directly into thecalibration controller 22 by a user.

At block 26, the projection area of the display screen 18 on which thefinal image is to appear is provided to the calibration controller 22.This area can be entered directly into the calibration controller 22 bythe user. Alternatively, if there are obvious physical delimiters at theedges of the projection area, the calibration controller 22 may generatethis area automatically.

Camera 20 may be located at the eye point of the display screen 18,which is generally the location that a viewer is expected to occupyduring a presentation, or alternatively, may be located elsewhere asindicated by decision block 28. If camera 20 is not located at the eyepoint, the orientation of the camera is determined, as indicated at step30, in order to correct for distortion caused by the camera position.The geometry distortion caused by the camera not being located at theeye point is referred to as a keystoning effect. An example of thekeystoning effect is shown in FIG. 5 in which a first vertical boundary42 of a rectangular projection area appears to be significantly shorterthan a second vertical boundary 44 of similar length. Camera orientationand position is generally determined by taking a number of key referencepoints for which both the actual position and the position in the cameraimage is known. The number of reference points used is typically threeand the reference points often correspond to corners of the projectionarea. Using the three reference points, the orientation of a viewingplane, which is defined as the plane having a normal equal to theorientation vector of the camera 20, is determined. Alternatively, theorientation of the camera 20 may be specified by the user directly. Withthe camera position and orientation known, target points can beprojected onto the viewing plane of the projector to compensate for thekeystoning caused by the displacement of the camera.

When camera 20 is located at or near the eye point, the multipleprojector system 10 automatically compensates for distortions in thegeometry without requiring a definition of the distortion. Distortionsinclude bumps or irregularities, for example, or any differences betweenthe actual screen geometry and the defined screen geometry.

At block 32, target reference marker locations are calculated using thecamera orientation information and the projection area. For eachprojector 16, the target reference markers form an evenly spaced matrixacross a projection field, which is generally defined as the portion ofthe final image that is projected by each respective projector 16.

Once the reference marker locations have been established, the geometrycorrection process 34, which is shown in FIG. 6, is performed. Thegeometry correction process 34 is performed for each projector 16, insequence. At block 46, the size of a single marker in camera space isdetermined by projecting a reference marker at the center of theprojection field of the projector 16 and taking an image of thereference marker. The marker size is dependent on several factorsincluding the distance from the projector 16 to the display screen 18,the type of lens mounted on the projector 16 and the relative imageresolutions of the projector 16 and camera 20. In addition to being usedin the calibration process, the marker size is also used in later imagesto filter noise from the image.

At block 48, the pixels in the camera image that correspond to thecorners of the projection area are determined. The corresponding pixelsmay be determined by the user and input to the calibration controller22, or the corresponding pixels may be determined automatically by thecalibration controller 22. In order for the pixels to be determinedautomatically by the calibration controller 22, the corner areas shouldbe clearly identifiable in the image, for example, a black bordersurrounding the screen.

Once the marker size has been established and the corners located, thecenter of the projector 16 is located, as indicated at block 50. Thecenter of the projector 16 is not necessarily the center of theprojection area in which the final image will be presented since theovershoot of the projectors may not be symmetric.

At block 52, the projector center point is used to generate an initialposition for a matrix of reference markers to be projected onto thedisplay screen 18 by the projector 16.

An image is captured by camera 20 of the initial position of the markerson the display screen 18, as indicated at block 54. At block 56, theimage is processed by the calibration controller 22 and the referencemarker locations are compared to the target reference marker locations,which were determined at step 32 of FIG. 3. If the distance between thereference markers and the respective target reference markers is greaterthan an acceptable distance, a feedback loop 58 is entered and at block60, new reference marker positions are calculated. The new referencemarker positions are projected onto the display screen 18 at block 52and another image is taken by camera 20 at block 54. The new referencemarker locations are then compared to the target reference markerlocations at block 56. The iterative process of feedback loop 58continues until the distance between the reference markers and thetarget reference markers is acceptable and final reference markerlocations are established. The acceptable distance is typically aprojector pixel, however, this distance may be adjusted by the user.

The final reference marker locations are used to produce a lookup tablethat is sent to each projector 16, as indicated at block 64. The lookuptable is generally a reverse map that maps output pixels to inputpixels. For example, for pixel (4, 10) in the final image, the lookuptable defines which pixel on the image incoming from the image generator12 is to be displayed at that point. The reverse map is generateddirectly from the reference marker locations. Alternatively, thereference marker locations may be used to generate a forward map thatmaps input pixels to output pixels, which in turn may be used togenerate a reverse map by interpolating through the forward map. Aforward map is generally easier to read and understand than a reversemap. Therefore, the forward map may be more desirable if the user wishesto make modifications to the geometry manipulation.

At block 66, the geometry calibration process for the first projector 16is complete. For an embodiment having a single projector 16, thegeometry calibration process is complete. For the multiple projectorsystem 10 of FIG. 2, the calibration process is then performed for eachremaining projector 16. Once all of the projectors 16 have beencalibrated, the multiple protection system 10 is ready to receive imagesfrom the image generator 12 and project them onto display screen 18 sothat they appear geometrically correct to an audience.

It will be appreciated by a person skilled in the art that the accuracyof the initial estimate for the location of the matrix of referencemarkers to be projected onto the display screen 18 by each projector 16does not affect the quality of the final result. However, the moreaccurate the initial estimate, the more quickly the system 10 willconverge on the target locations.

Referring to FIG. 7, a block diagram of an embodiment of the multipleprojector system 10 for use with non-planar display screens 18 is shown.At block 68, the layout of the projection system 10 is sent to thecalibration controller 22. At block 70, a definition of the non-planarprojection surface is provided to the calibration controller 22. Theprojection surface may be defined by an equation, an explicit discretesurface file or another suitable type of surface definition.

At decision block 72 the location of the camera 20 is determined. If thecamera 20 is not located at the eye point, a desired eye point isprovided to the calibration controller 22 at block 74. The matrix ofreference markers is calculated at block 76. Using the definition of thenon-planar projection surface and the desired eye point, the system 10is able to determine, in three dimensions, where the matrix of markersshould appear on the display screen 18. At block 78, the threedimensional reference markers are then projected onto the viewing planeof the camera 20 and converted into camera coordinates. The previouslydescribed geometry correction process 34 may then be performed.

Because the system is iterative, some distortions in the geometry of anon-planar projection area will automatically be compensated for, suchas imperfections in a simple or compound curved screen, for example. Itwill be appreciated by a person skilled in the art that as theirregularity of the surface increases, the resolution of matrix markersshould also increase in order to produce adequate results.

In order to produce a final image on the display screen 18 that is notonly geometrically correct but also appears seamless, the projectors 16perform color correction on the incoming pixels. For proper colorcorrection between multiple overlapping projectors 16, brightness anduniformity, color and gamma should be all be matched. A colorcalibration process, which is described in relation to FIGS. 8, 9 and10, is performed by the calibration controller 22 to calculate correctedcolor values for each projector 16.

Brightness and uniformity matching is performed in two phases as shownin FIGS. 8 and 9, respectively. In the first phase, an iterativeuniformity matching process 80 is performed for each projector 16.Camera 20 captures the projected image and various points on the imageare sampled by the calibration controller 22. The intensity of thesampled points is then compared. If the intensity is not equal acrossthe points, or within a predetermined threshold, the intensity of thebrighter regions is reduced to match the lowest intensity. The process80 is repeated until the brightness is generally uniform across theprojector's image. Once all of the projectors 16 have undergone theuniformity matching process 80, intensity matching 82 is performed.

In the second phase, the intensity matching process 82 is performed foreach projector 16. An intensity value of each projector 16 is sampled bythe camera 20, as indicated by reference numeral 84, and the projector16 having the lowest intensity is determined, as indicated at block 86.Sampling generally consists of capturing an image of an area covering aportion of the projected image with the camera 20, and sampling andaveraging numerous values from the image captured. An iterative process88 is then performed to reduce the intensities of each projector 16 tomatch the lowest intensity level. Projector lamp power, projectoraperture and the number of lamps used by the projector are iterativelyre-sampled and adjusted. Specifically, projector lamp power is adjustedfirst, followed by projector aperture. If adjustment of these variablesis insufficient, the variables are restored to their default values andone of the lamps in a multiple lamp projector is turned off. The processis then restarted by adjusting projector lamp power.

It will be appreciated that the first phase may be bypassed if theprojector 16 has uniform brightness across its projection field.

Matching the color between projectors 16 is also performed in twophases. In the first phase, a common color gamut is calculated and inthe second phase all projectors 16 are matched to this gamut. Aprojector's color gamut is the range of possible colors it is able toproduce. Gamuts are commonly represented as areas in a CIE 1931chromaticity diagram. A common color gamut is a gamut that can beachieved by all projectors in the multiple projector system 10.

Referring to FIG. 10, a color gamut determining process 90 is performedfor each projector 16. The projector 16 is first set to the maximumcolor gamut that it can produce. The camera 20 then samples points onthe projected image for each primary color (red, green, blue) andaverages the sampled values to calculate a color gamut in camera space.A common color gamut is then calculated using the color gamutinformation obtained from each projector 16, as indicated at block 92.

An iterative color gamut matching process 94 is then performed. For eachprimary color, the projected image is captured and sampled values arecompared to the common color gamut. If the sampled values are not equalto corresponding values on the common color gamut, a color change iscalculated and applied to projector 16. This process 94 is repeateduntil the sampled values are equal to, or within a predeterminedthreshold, of the common color gamut.

For gamma matching, a gradient test pattern in which a number of barsranging in color from white, or a primary color, to black, is used.First, one projector of the multiple projector system 10 is selected asthe baseline projector. Each bar in a test pattern of the baselineprojector is then sampled and compared to corresponding bars on each ofthe other projectors 16. The gamma values of the other projectors arethen adjusted until the brightness of each bar in the test pattern fallswithin a certain tolerance of the baseline projector brightness. Inorder for each particular bar to be properly exposed so that the camera20 is able to differentiate between adjacent bars on the test pattern,the exposure time and aperture settings on the camera 20 may beadjusted. Available color depth for the camera 20 and number of gradientbars in the test pattern generally determine whether or not cameraadjustments will be required.

Once geometry, brightness, color and gamma corrections are applied, theoverlap areas between the images projected by the respective projectors16 are blended. The blending process includes the application ofmechanical and/or electronic blinders. Generally, mechanical blinderstypically perform better when darker scenes are projected and electronicblinders typically perform better when brighter scenes are projected.The electronic blinders are applied within the warping systems of therespective projectors 16. Referring to FIG. 11, for each projectorintersection, or overlap area, a blending process 124 is performed.First, a default blending shape and intensity change is calculated, asindicated at block 126. The default blending shape and intensity changeare calculated based on the geometry correction information that waspreviously determined. Then, at block 128, the blend is applied and animage is captured of the overlap area. If the blend is acceptable, thesettings are saved in the projectors 16, as indicated at block 132. Ifthe blend is not acceptable, an iterative blend calculation loop isentered and the blend calculations are modified at block 130. Theprocess is repeated until the brightness across the entire overlap areais generally even.

Since mechanical blinders perform better for dark scenes, a system inwhich the blinders are placed and removed automatically may be used.Such a system is described in U.S. application Ser. No. 11/189,836,which was filed Jul. 27, 2005 and assigned to Christie Digital SystemsInc. For this type of system, the blending process 124 is performed bothwith and without blinders in place and both results are stored.

Referring back to FIG. 2, the dashed lines represent communication thatoccurs between the multiple projector system 10 and the calibrationsystem 11 during the geometry calibration process of FIGS. 3, 6 and 7and the color calibration process of FIGS. 8, 9 and 10. The solid linesshown represent communication that occurs during regular operation ofthe multiple projection system 10. As shown, the calibration system 11is independent of the multiple projector system 10 and is not requiredonce the multiple projection system 10 has been calibrated. Once themultiple projector system 10 has been calibrated, images from the imagegenerator 12 are corrected in real time by the projectors 16. Thecalibration controller 22 and the camera 20 are selected so that thecalibration system 11 is portable and thus may be taken to any number ofdifferent sites to perform calibration. This may result in significantcost savings for the user since it is not necessary to purchase thecalibration system 11 in order to use the multiple projector system 10.The calibration system 11 may be borrowed or rented instead.

Referring to FIG. 12, another embodiment of a multiple projection system110 and a calibration system 111 is shown. The calibration system 111includes a calibration controller 122 that receives images from a camera120 and generates geometric calibration data color calibration data ashas been previously described. The multiple projection system 110includes an image generator 112 that provides image information fordisplay on a display screen (not shown). The image information passesthrough video feed lines 114 to a warping system 102, which includeswarping modules 104. The warping modules 104 alter the image informationbased on the calibration data and send the corrected image informationto respective projectors 116 through a second set of video feed lines115. Each projector 116 then projects a corrected image (not shown) onthe display screen. Unlike the embodiment of FIG. 2, the projectors 116do not include color modification and geometry manipulation functions.Instead, the projectors 116 are generic projectors not capablethemselves of geometry correction, such as the Christie Matrix 3500, forexample. This type of projector simply projects a pre-corrected image.

The multiple projection system 110 operates in a similar manner as themultiple projection system 10 of FIG. 2, however, the color modificationand geometry manipulation is performed by the warping system 102 andcorrected image data is sent to the projectors 116. The dashed lines ofFIG. 11 represent communication that occurs during the calibrationprocess defined in FIGS. 3 and 6 to 10 and the solid lines representcommunication that occurs during regular operation of the multipleprojection system 100. Similar to the previous embodiment, once themultiple projector system 110 has been calibrated, images from the imagegenerator 112 are corrected in real time by the warping system 102.

Although the warping modules 104 are shown as individual units in FIG.12, it will be appreciated that the warping system 102 may bemanufactured as a single unit.

The calibration system of the present invention is not limited to usewith projectors only. It will be appreciated by a person skilled in theart that any suitable image producing device may be used including amonitor, a display panel or a Liquid Crystal Display (LCD) screen, forexample.

A specific embodiment of the present invention has been shown anddescribed herein. However, modifications and variations may occur tothose skilled in the art. All such modifications and variations arebelieved to be within the sphere and scope of the present invention.

What is claimed is:
 1. A system comprising: a plurality of projectors; acamera for capturing images provided at a screen by the plurality ofprojectors; and, a computer for: implementing a calibration processcomprising: capturing, using the camera, a projected image of a matrixof reference markers projected by the plurality of projectors on thescreen; comparing locations of the reference markers in the projectedimage with target reference marker locations stored as a staticgeometrically correct image, the static geometrically correct imageindependent of any data captured by the camera; and, calculating newestimated locations for the reference markers; iteratively repeating thecalibration process until the reference markers are within apredetermined distance of the target reference marker locations toproduce calibration data; and, communicating at least a portion of thecalibration data to each of the plurality of projectors to correctfurther images to be projected on the screen.
 2. The system of claim 1,wherein each of the plurality of projectors comprises a respectivewarping system for warping geometry of the projected image and thefurther images.
 3. The system of claim 1, further comprising an imagegenerator for providing at least the further images to the plurality ofprojectors.
 4. The system of claim 1, wherein each of the plurality ofprojectors is further configured to map pixel locations in the furtherimages to corrected pixel locations based on the calibration data, tocorrect the further images.
 5. The system of claim 1, wherein thecalibration data is provided in a lookup table.
 6. The system of claim1, wherein the calibration process further comprises one or more of: acolor calibration process; an intensity matching process; and, ablending process for matching brightness in overlap areas of the imagesprovided at the screen by each of the plurality of projectors.
 7. Thesystem of claim 1, further comprising the screen.
 8. A systemcomprising: a plurality of projectors; a camera for capturing imagesprovided at a screen by the plurality of projectors; and, a computerfor: implementing a calibration process comprising: comparing aprojected image at the screen with a static geometrically correct image,the projected image captured by the camera, the static geometricallycorrect image independent of any data captured by the camera; and,correcting the projected image based on the comparing; and, iterativelyrepeating the calibration process until features in the projected imageare located within a predetermined distance of target feature locationsin the static geometrically correct image; and, generating calibrationdata for mapping further images to be projected on the screen onto thestatic geometrically correct image, each of the plurality of projectorsfor correcting the further images based on the calibration data.
 9. Thesystem of claim 8, wherein each of the plurality of projectors comprisesa respective warping system for warping geometry of the projected imageand the further images.
 10. The system of claim 8, further comprising animage generator for providing at least the further images to theplurality of projectors.
 11. The system of claim 8, wherein each of theplurality of projectors is further configured to map pixel locations inthe further images to corrected pixel locations based on the calibrationdata, to correct the further images.
 12. The system of claim 8, whereinthe calibration data is provided in a lookup table.
 13. The system ofclaim 8, wherein the calibration process further comprises one or moreof: a color calibration process; an intensity matching process; and, ablending process for matching brightness in overlap areas of the imagesprovided at the screen by each of the plurality of projectors.
 14. Thesystem of claim 8, further comprising the screen.
 15. A methodcomprising: at a system comprising: plurality of projectors; a camerafor capturing projected images provided at a screen by the plurality ofprojectors; and, a computer, implementing, at the computer, acalibration process comprising: capturing, using the camera, a projectedimage of a matrix of reference markers provided by the plurality ofprojectors at the screen; comparing locations of the reference markersin the projected image with target reference marker locations stored asa static geometrically correct image, the static geometrically correctimage independent of any data captured by the camera; and, calculatingnew estimated locations for the reference markers; iteratively repeatingthe calibration process until the reference markers are within apredetermined distance of the target reference marker locations toproduce calibration data; and, communicating at least a portion of thecalibration data to each of the plurality of projectors to correctfurther images to be provided at the screen.
 16. The method of claim 15,wherein the calibration process further comprises one or more of: acolor calibration process; an intensity matching process; and, ablending process for matching brightness in overlap areas of the imagesprovided at the screen by each of the plurality of projectors.
 17. Themethod of claim 15, further comprising further mapping pixel locationsin the further images to corrected pixel locations based on thecalibration data, to correct the further images
 18. A method comprising:at a system comprising: a plurality of projectors; a camera forcapturing display images provided at a screen by the plurality ofprojectors; and, a computer, implementing, at the computer, acalibration process comprising: comparing a projected image at thescreen with a static geometrically correct image, the projected imagecaptured by the camera, the static geometrically correct imageindependent of any data captured by the camera; and, correcting theprojected image based on comparing; and, iteratively repeating thecalibration process until features in the projected image are locatedwithin a predetermined distance of target feature locations in thestatic geometrically correct image; and, generating calibration data formapping further images to be provided to the screen onto the staticgeometrically correct image, each of the plurality of projectors forcorrecting the further images based on the calibration data.
 19. Themethod of claim 18, wherein the calibration process further comprisesone or more of: a color calibration process; an intensity matchingprocess; and, a blending process for matching brightness in overlapareas of the images provided at the screen by each of the plurality ofprojectors.
 20. The method of claim 18, further comprising furthermapping pixel locations in the further images to corrected pixellocations based on the calibration data, to correct the further images